Catalytic alkylation method and apparatus with hydrocarbon recycle

ABSTRACT

A process and apparatus for the catalytic alkylation of an isoparaffin with one or more olefins. Reactant hydrocarbons are passed in contact with a liquid catalyst such as hydrofluoric acid in a reaction zone. The hydrocarbon phase is allowed to separate from the catalyst phase in a settling zone, and a portion of the hydrocarbon phase is cooled and reintroduced to the reaction zone in a separate stream from that of the feed hydrocarbons. The alkylation apparatus by which the process is carried out includes a vertical reaction vessel, which in a preferred embodiment is 2 to 6 feet in height, a settling vessel, means for fluid flow from the reaction vessel to the settling vessel, a conduit for fluid flow between the upper part of the settling vessel and the reaction zone, and means for cooling fluid in this conduit.

BACKGROUND OF THE INVENTION

This invention relates to the catalytic alkylation of an isoparaffinwith one or more olefins. It further relates to apparatus for carryingout alkylation.

The catalytic alkylation of an isoparaffin with one or more olefins toproduce a branched chain paraffin is a commercially important processfor producing high-octane gasoline. Conventional catalytic alkylationprocesses generally involve the reaction of an isoparaffin such asisobutane with an olefin such as propylene and/or a butylene in thepresence of a liquid alkylation catalyst, followed by the separation ofthe unreacted and product hydrocarbons from the catalyst in a settlingzone and purification of the product alkylate. Because of the exothermicnature of the reaction, it is necessary to provide means of controllingthe temperature inside the reaction vessel and maintaining the optimumalkylation temperature. Methods of maintaining this temperature includerecycling the catalyst from the settling zone through a cooler and backto the reaction zone and recycling hydrocarbons from the settling zonethrough a cooler to be added to the hydrocarbon feed stream. Because ofthe corrosiveness of the catalysts used in alkylation, it is desirableto minimize catalyst circulation. It is also desirable to design thealkylation system so as to produce an alkylate which has a high octanerating.

Alkylation reaction apparatus known as open-pipe riser reactors comprisea vessel in which feed hydrocarbons are emulsified with liquid catalyst.The intimate contact between acid catalyst and hydrocarbons necessaryfor efficient reaction between olefin and paraffin is provided byinjecting the hydrocarbons into the reactor through high-pressurenozzles in the form of a fine dispersion. Commercial open-pipe riserreactors are generally 20 to 40 feet in height and 2 to 4 feet indiameter. It is desirable in terms of economy and maintenance to reducethe size of commercial reactors and to minimize the flow of acidcatalyst while maintaining the quality of the alkylate produced.

It is thus an object of this invention to provide an alkylation processand apparatus in which a high-octane alkylate is produced and acidcirculation is minimized.

It is a further object of one aspect of the invention to providerelatively small alkylation apparatus.

SUMMARY OF THE INVENTION

According to the invention, an isoparaffin is alkylated with at leastone olefin in the presence of an alkylation catalyst in a reaction zone,the reaction effluent separates into a hydrocarbon phase and a catalystphase in a settling zone, and a portion of the hydrocarbon phase iscooled and introduced into the reaction zone separately from thehydrocarbon feed stream.

Further according to the invention, an alkylation riser reactor isprovided which comprises a vertical reaction vessel, a settling vessel,means for fluid flow from the reaction vessel to the settling vessel,means for fluid flow between the upper part of the settling vessel andthe reaction zone, and means for cooling the fluid in this conduit. In apreferred embodiment, the vertical portion of the reaction vessel is twoto six feet in height and has an integral settling zone in a horizontalvessel openly connected to the upper portion of the vertical reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a simplified schematic flow diagram of the inventionprocess showing the preferred form of the alkylation apparatus.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the invention, an isoparaffin is reacted with at leastone olefin in the presence of a catalyst under conditions which maintainreactants and catalyst in the liquid phase. The isoparaffin can be anyalkylatable isoparaffin such as isobutane or isopentane and the olefincan be a low molecular weight olefin such as propylene, a butylene, anamylene, and like hydrocarbons, or a mixture of these. The alkylationcatalyst is generally an acid-acting liquid such as sulfuric acid,hydrogen fluoride, phosphoric acid, a halosulfonic acid and aluminumchloride. Hydrogen fluoride is the preferred catalyst because of itsability to be reused and because of the superior quality of the alkylateproduced. The hydrogen fluoride catalyst used is generally 85 to 98weight percent HF and 2 to 15 weight percent water, acid-soluble oilsand hydrocarbons. The alkylates produced are branched paraffins,generally isomers of heptane, octane and like hydrocarbons.

The process of the invention can be described more fully by reference tothe FIGURE, which illustrates an embodiment of the invention in whichliquid isobutane is alkylated with a liquid mixture of propylene andbutylenes in liquid hydrogen fluoride catalyst.

A stream of olefins 3 generally at about 80° F. or ambient temperatureis mixed with a stream of feed or fresh isobutane 4 and a stream ofrecirculated isobutane 5, and the resulting combined feed stream 6 isdivided into individual streams 7 and injected into reaction vessel 1through high pressure nozzles 8. The feed mol ratio of isobutane toolefin (including both fresh isobutane and isobutane recirculated foraddition to the feed stream) will generally be in the range 2:1 to 30:1,optimally for commercial operations about 10:1 to 12:1 for production ofhigh-octane alkylate. The hydrocarbon stream is introduced directly intocatalyst phase 2 in the form of a fine dispersion. The nozzle velocity,opening diameter and pressure drop across the nozzle determine dropletsize and degree of dispersion. Depending upon the size of the reactor,the feed can be introduced through 1 to 200 nozzles each having anopening diameter of 0.01 to 0.60 inch. The pressure drop across eachnozzle can vary from 20 to 100 psig, but is generally 24-45 psig, andnozzle velocity is within the range of about 10 to about 125 feet persecond. The resulting hydrocarbon droplet size will generally be in therange of 10 to 1000 microns, preferably 10 to 100 microns to give goodcontact with the catalyst. The level of the catalyst above the nozzlesand the fineness of the spray can be adjusted to give the residence timeof reactants in the reaction zone which gives maximum octane value forthe product. Although the residence time of hydrocarbons in the reactionzone can vary widely depending upon the variables discussed above, thepractice of the invention in the preferred apparatus will permitresidence times of 30 to 120 seconds, optimally about 80 seconds.

Pressure in the reaction zone will be about 120 to 200 psig, sufficientto maintain the reactants in the liquid phase.

The reacting hydrocarbons and reaction products rise in the reactorthrough the liquid catalyst. The reaction effluent containinghydrocarbons, fluorocarbons, and catalyst can be withdrawn from theupper portion of the vertical reactor and fed into a settling tank forseparation of the hydrocarbon phase from the catalyst phase. In theembodiment illustrated in the FIGURE, the settling zone is located inthe upper portion of the reactor, in a horizontally-elongated tankopenly connected with the top of the vertical reaction zone. In thissettling zone, the reaction effluent is continuously separated into anupper liquid hydrocarbon phase 13 comprising alkylation products andunreacted isoparaffin, and a lower liquid catalyst phase.

A portion of the hydrocarbon phase is passed via conduit 14 to aseparation zone 15 where the product alkylate is separated fromunreacted isobutane, normal butane, propane and catalyst. The separationof the components of the alkylate stream conventionally includes severalfractionation steps. Isobutane recovered from the hydrocarbon stream iscooled and recycled in stream 5 to be combined with feed olefins andfresh isobutane for reintroduction into the reactor. It is within thescope of the invention to combine at least a portion of isobutanerecycle stream 5 with the cooled hydrocarbon recycle stream 9 for directinjection into the reaction zone. This would require the decrease innozzle orifice size to attain the same pressure drop across the feedhydrocarbon nozzles.

The portion of hydrocarbon phase 13 which is not fed to thefractionation zone for alkylate recovery is removed in stream 9, eitherdirectly from the settling zone or via 16 from hydrocarbon stream 14.Stream 9 is cooled in 10, which can be any conventional heat exchangeunit such as a shell-tube heat exchanger, to about 80° F. or to thetemperature necessary to maintain the optimum reaction temperature inthe reaction zone. The cooled hydrocarbon stream is reintroduced intoreactor 1 separately from the combined feed stream 6. In commercialoperations, the inlet velocity of the recycled hydrocarbons will beabout 0.1 to about 5 feet per second. There can be from 1 to about 20inlets for recycled hydrocarbon, with each inlet opening being from0.125 inch to about 6 inches in diameter. The FIGURE shows the recycledhydrocarbon stream divided into two streams 11 and 12, but the number ofrecycled hydrocarbon streams entering the reactor can vary widelydepending upon the particular reaction conditions and the size of thereactor. The cooled hydrocarbon stream aids in maintaining the desiredreaction temperature in the reactor, which is generally 70° to 90° F.but can range from 40° to 120° F., the higher temperatures generallyapplying to propylene alkylation. In the embodiment illustrated in FIG.1, the hydrocarbon recycle streams are injected at right angles to thedirection of injection of mixed feed stream 6. Each recycle stream isintroduced into the reactor at approximately the same catalyst level asthe level of introduction of the combined feed stream, the level ofentry being within 12 inches above or below the catalyst level of thefeed nozzle outlets. This hydrocarbon recycle stream containspredominantly isobutane, but also includes organic fluorides, propane,normal butane and alkylate. It is believed that, in the reaction zone,organic fluorides in this stream react with isobutane in the presence ofhydrocarbon fluoride to produce additional alkylate, releasing HF in theprocess.

As needed to maintain catalyst concentration in the reactor, catalystcan be intermittently or continuously removed via 17 to a rerun unit(not shown) to remove acid-soluble oils and water by distillation. Rerunand/or makeup catalyst can be added to the reactor through 18. Thecatalyst bed is essentially static, i.e., there is no appreciablecontinuous external circulation of catalyst. It is known that inlarge-scale riser reactors there is a tendency of the catalyst to movedown along the walls of the vessel, so that there is a form of internalcirculation of catalyst upward with the reacting hydrocarbons anddownward along the sides of the reactor.

The reactor which can be used in the practice of the process of theinvention is shorter in height and larger in diameter relative to heightthan conventional alkylation riser reactors, which are generally about40 feet in height and about 2.5 feet in diameter. The invention reactorcan, for example, have a diameter to height ratio of about 1:14 to 1:1,although the actual dimensions may vary widely depending upon the othervariables in the alkylation system. The height of the vertical portionof the vessel can range from 2 to 6 feet, and the diameter can be 0.14to 5 feet.

The FIGURE also illustrates an embodiment of the alkylation reactionvessel of the invention. Reaction vessel 1 has a lower vertical portion22 into which isobutane and olefins in combined feed stream 6 areinjected through nozzles 8 having a nozzle velocity of about 50 feet persecond. The nozzle for commercial operations can be any suitable nozzlewhich can produce a fine dispersion of hydrocarbon, such as SprayingSystems Company WhirlJet nozzle Type B having a 3/64 inch to 5/8 inchdiameter orifice. The number of nozzles and orifice size used depends onthe pressure drop across the nozzle desired, nozzle velocity desired andquantity of liquid charged to the reactor. Hydrocarbons recycled in line9 according to the invention process are introduced into the lowerportion of the reaction vessel. The hydrocarbons can be introducedthrough a nozzle or, as shown in the drawing, directly into the reactorthrough an opening in the reactor wall. In the illustrated embodiment,the introduction of the recycle stream into the catalyst is at rightangles via lines 11 and 12 to the introduction of mixed feed stream 6via nozzles 8. Separation of the lighter hydrocarbon phase from thedenser acid phase takes place in the upper horizontal portion 21 of thereactor. The hydrocarbon phase can be removed through line 14 in theupper portion of horizontal settling zone 21. The recycle portion of thehydrocarbon phase can be removed in line 9 or, alternatively, in line16. This recycle hydrocarbon stream is pumped by conventional pump 23through heat exchanger 10 and back into the reaction vessel.

Table I presents process conditions and yields for a test run carriedout according to the process of the invention. In this run, liquidisobutane was alkylated with liquid butylenes in liquid hydrogenfluoride catalyst. The reactor used for this test run was a small-scaleexperimental model of a riser reactor which was about 49 mm in diameterand about 700 mm in height. One nozzle for introduction of the combinedfeed stream was used. The opening diameter for this nozzle was 0.38 mm(0.015 inch) and the pressure drop across the nozzle was 37 psi (240kPa). One lateral recycle hydrocarbon stream having an opening diameterof 9.3 mm (0.364 inch) was introduced at a point slightly below thelevel of the outlet of th feed nozzle.

                  TABLE I                                                         ______________________________________                                         Operation:                                                                   ______________________________________                                        Feed Olefin, gallons/hr.                                                                          0.062                                                     Composition, volume %                                                         Butene-1            22.4                                                      Isobutylene         28.3                                                      Butenes-2           49.3                                                      Feed Isobutane, gallons/hr.                                                                       0.258                                                     Composition, volume %                                                         Propane             0.34                                                      Isobutane           96.09                                                     Normal butane       3.57                                                      Recycle Isobutane, gallons/hr.                                                                    1.27                                                      Composition, volume %                                                         Propane             0.66                                                      Isobutane           98.76                                                     Normal butane       0.58                                                      Recycle Hydrocarbon, gallons/hr.                                                                  11.1                                                      Composition, volume %                                                         Propane             0.65                                                      Isobutane           91.64                                                     Normal butane       1.17                                                      Pentane plus        6.54                                                      HF Catalyst                                                                   Volume, gallons     0.75                                                      Composition, wt. %                                                            HF                  90.6                                                      H.sub.2 O           3.7                                                       Acid Soluble Oils   0.2                                                       Hydrocarbons        5.5                                                       Feed plus recycle isobutane/olefin                                            mol ratio            24:1                                                     Total IC.sub.4 /Olefins, Volume Ratio                                                             188:1                                                     Hydrocarbon Recycle/Olefins,                                                  Volume Ratio        180:1                                                     Total of all Hydrocarbon/HF                                                   Catalyst Volume Ratio                                                                             2.8:1                                                     Volume of Total Hydrocarbon per                                               Volume of Catalyst/hr.                                                                            17                                                        Reaction Temperature, °F.                                                                  80                                                        Reaction Pressure, psig                                                                           148                                                       Debutanized Alkylate                                                                              96.0      (Research                                                                     Octane, 0 cc                                                                  TEL)                                            Nozzle Velocity (Combined                                                     feed stream), ft/sec                                                                              50                                                        Orifice Velocity (Recycle                                                     hydrocarbon stream), ft/sec                                                                       0.6                                                       ______________________________________                                    

The following runs were performed in the test reactor and providecomparisons of the invention process with other alkylation processes.For those runs in which there was no hydrocarbon recycle, the acidcatalyst was cooled and recycled to the reactor.

A run was performed using the mixed butylenes (butene-1, butene-2 andisobutene) of the invention run shown in Table I, except that cooledacid circulation from the settling zone to the reaction zone wassubstituted for cooled hydrocarbon recirculation. The RON clear(research octane number, 0 cc tetraethyl lead) of the alkylate producedin this run was about 94.9. An improvement of 1.1 octane numbers thusresulted from cooling the hydrocarbon stream and reintroducing it intothe reaction zone, rather than using an acid cooling stream and nohydrocarbon recycle as in the comparative run.

Similar runs were performed with propylene using anisobutane-to-propylene feed ratio of 29:1. When the run was performedwith no hydrocarbon recycle, the RON clear was about 91.25; withhydrocarbon recycle from the settling zone directly into the reactionzone, the RON clear value of the alkylate was about 91.65. While thepractice of the invention thus resulted in an improvement in octanerating of the product, the advantage in terms of the octane of thealkylate was not as pronounced in the propylene run as in the butylenerun described above.

Test runs were also performed in the experimental reactor using a 44/56weight ratio mixture of propylene/butylenes. The isobutane-to-olefinfeed ratio was 10.5/1. When this mixed olefin feed was charged to thereaction zone through the nozzle with no hydrocarbon recycle employed,the RON clear of the alkylate was about 92.8. When the run was repeatedwith a hydrocarbon recycle stream injected into the reaction zonethrough the nozzle, that is, combined and introduced as part of the feedstream (resulting in an isobutane-to-olefin ratio of 22:1), the alkylateproduced had a RON clear octane number of 92.7. Similar runs were thenperformed using isobutane-to-olefin ratios of 6.7:1 (without hydrocarbonrecycle) and 18.0:1 (with hydrocarbon recycle through the nozzle), withresulting alkylate octane numbers of 92.7 and 92.4, respectively.Because of the different olefin feed and the differentisobutane-to-olefin ratios used in these mixed olefin runs as comparedwith the invention runs using butylenes and propylenes described above,no direct comparison of the runs was made. However, based on the dataobtained for mixed olefins which shows that, in the test reactoremployed and under the reaction conditions which existed, there was noimprovement in octane number when the hydrocarbon phase was recycledthrough the feed nozzle as compared with when the hydrocarbon phase wasnot recycled at all, the inference can be drawn that hydrocarbon recycledirectly into the reaction zone according to the invention represents animprovement over recycle to the feed stream and introduction into thereaction zone via the feed nozzle.

We claim:
 1. An alkylation process comprising the steps of:(a) injectinga feed hydrocarbon stream comprising an isoparaffin and at least oneolefin into an alkylation catalyst bed in an alkylation zone underconditions suitable for producing an alkylate, and producing analkylation effluent comprising the alkylate and the alkylation catalyst;(b) passing the alkylation effluent to a phase separation zone andtherein forming an upper liquid hydrocarbon phase comprising thealkylate and unreacted isoparaffin and a lower alkylation catalystphase; (c) withdrawing, as a recycle hydrocarbon stream, a first portionof the liquid hydrocarbon phase from the phase separation zone, coolingthe recycle hydrocarbon stream, passing the cooled recycle hydrocarbonstream to the alkylation zone, and injecting the cooled recyclehydrocarbon stream directly into the alkylation catalyst bed withoutprior contact with the feed hydrocarbon stream; (d) withdrawing, as aproduct stream, a second portion of the liquid hydrocarbon phase fromthe phase separation zone.
 2. The alkylation process of claim 1 whereinthe recycle hydrocarbon stream is injected into the alkylation catalystin the reaction zone at approximately right angles to the direction ofinjection of the feed hydrocarbon stream.
 3. The alkylation process ofclaim 1 further comprising the steps of(e) passing the product stream toa fractionation zone; (f) separating the unreacted isoparaffin from theproduct stream in the fractionation zone; and (g) passing the thusseparated unreacted isoparaffin from the fractionation zone to the feedhydrocarbon stream and injecting the unreacted isoparaffin into thereaction zone as a constituent of the feed hydrocarbon stream.
 4. Thealkylation process of claim 3 wherein at least a portion of theunreacted isoparaffin separated from the product stream in step (f) iscombined with the recycle hydrocarbon stream.
 5. The alkylation processof claim 1 wherein the alkylation catalyst is liquid hydrogen fluorideand the alkylation catalyst bed is essentially static.
 6. The alkylationprocess of claim 5 wherein the feed hydrocarbon stream is injected intothe alkylation zone through at least one nozzle in the form of a finedispersion.
 7. The alkylation process of claim 6 having a hydrocarbonresidence time in the alkylation zone of 30 seconds to 120 seconds. 8.The alkylation process of claim 6 wherein the recycle stream isintroduced into the reaction zone at a level in the alkylation catalystwhich is within 12 inches above or below the level in the alkylationcatalyst of the at least one nozzle.
 9. The alkylation process of claim1, claim 5 or claim 8 wherein the isoparaffin is selected from the groupconsisting of isobutane and isopentane and the olefin is selected fromthe group consisting of ethylene, propylene, isobutene and mixturesthereof.
 10. The alkylation process of claim 9 wherein the isoparaffinis isobutane and the olefin is selected from butene-1, butene-2,isobutylene, and mixtures of these.
 11. The alkylation process of claim10 wherein the reaction is carried out under a temperature of 40° to110° F. and a pressure of 120 to 200 psig.
 12. The alkylation process ofclaim 11 wherein the reaction temperature is maintained within the rangeof 70° to 90° F.
 13. The alkylation process of claim 12 in which theliquid hydrocarbon phase further comprises organic fluorides.